Light writes info into atoms

December 15/22, 2004

Researchers from the Danish Quantum Optics
Center, the Max Planck Institute for Quantum Optics, and the Free University
of Brussels in Belgium have demonstrated that it is possible to transfer
information encoded in the properties of photons to atoms.

The researchers showed that the transfered information could be
stored as long as four thousands of a second, which is long enough to
carry out computations on it. The method is efficient and has a fidelity,
or ability to avoid errors, that is higher than previous research efforts
to transfer information from photons to atoms, according to the researchers.

The method could be used to provide a buffer for information carried
by light signals. It could also be used as memory for quantum computers,
which use the attributes of particles like photons and atoms to compute.
Quantum computers have the potential to be many orders of magnitude faster
than conventional computers for certain types of very large problems,
including solving the difficult mathematics underlying most of today's
encryption codes.

The researchers demonstrated the method by transferring information
stored in a weak laser pulse to spin-polarized, or magnetically aligned,
cesium atoms.

They fired the laser pulse through a cloud of atoms, measured
the information-storing properties of the photons, then set a radio-frequency
magnetic pulse that, combined with the effect of the laser beam, transfered
the information to the atoms. Reversing the process allowed them to read
the information stored in the atoms.

The researchers' next steps include increasing the speed of information
transfer, implementing the memory in a solid rather than a gas, and demonstrating
that the memory can work for the entangled and single-photon states used
by quantum computers.

The quantum memory could be used in practical applications and
5 to 15 years, according to the researchers. The work appeared in the
November 25, 2004 issue of Nature.